1. Field of the Invention
The present invention relates to a paper feed apparatus for use in an image forming apparatus or the like. More particularly, the present invention relates to a paper feed apparatus usable with an image forming apparatus such as an electronic or electrostatic copying machine, a simple printing machine or the like, which is provided with a cassette type paper feeder.
In such a paper feed device for the papercontaining cassette, the cassette, which is pre-loaded with a stack of cut paper sheets, is inserted into the cassette receiving opening in the apparatus body. The cut sheets are fed from the cassette into an image formation section in the apparatus one by one under the action of paper feed means which is provided in the apparatus. By preparing a plurality of cassettes which contain the respective stacks of cut sheets different from one another in size and material, one cassette can manually and simply be replaced by another cassette so that any stack of cut sheets will be selected in response to the requirement of size and/or material for cut sheets. If a plurality of such cassettes can simultaneously be mounted within the apparatus so that one of them can automatically be selected simply by depressing a selector button, it is convenient in that the selection of cut paper sheets can more simply and easily be carried out in response to the requirement of size and/or material for cut sheets.
2. Description of the Prior Art
In paper cassettes which have currently been used for such a purpose, the accommodation capacity is 250 or 500 sheets at maximum. If a number of copies, for example, 1000 or 2000 are to be continuously made, several supplies of paper must cumbersomely be carried out to that cassette. In each supply of paper, the copying operation is unavoidably interrupted so that a high speed capability of a copying machine will unsatisfactorily be utilized.
There are known some high-grade and high-speed copying machines of such a type that a large-sized deck or tray is used to contain and feed a number of paper sheets, for example, 2000. Such a deck or tray mechanism is exclusively mounted in that copying machine, so that is cannot be used in an other copying machine of a different type.
As disclosed in Japanese Laid-open Patent Application No. 17960/1982, there has recently been proposed an image forming apparatus in which, if a great number of paper sheets are required in an continuous operation, a paper feed device having an increased accommodation capacity can be connected with the image forming apparatus in place of a paper cassette having its reduced accommodation capacity and feed the paper sheets to the image forming apparatus as if the paper cassette did, without any change of specification in the image forming system. However, such a paper feed device has to be connected to the image forming apparatus. Therefore, there still remains some difficulties in that the paper feed device cannot widely and easily be used in various types of image forming apparatus.
In order to overcome the just mentioned problem, there has further been proposed a paper feed apparatus which comprises a large-sized paper-containing section accommodatable of a great number of cut paper sheets, a paper conveying section operatively connected with the paper-containing section and mountable into an image forming device through its entrance for the paper cassette, and a paper feeding mechanism for feeding the paper sheets from the large-sized paper-containing section to the paper conveying section one by one, whereby, when the previous paper sheet has been fed out of the paper conveying section under the action of paper feed means in the image forming device, a paper sheet can automatically be fed from the large-sized paper-containing section to the conveying section and then caused to wait in the conveying section. See Japanese Laid-open Patent Application No. 112247/1982.
The paper conveying section of this paper feed device is inserted into the cassette receiving opening of the conventional image forming system of paper-cassette insertion type having no built-in large-sized deck mechanism. Since the paper feed device includes its large-sized paper-containing section, the image forming apparatus continuously receives a number of cut paper sheets, for example, 1000 or 2000 from the paper-containing section so that the copying operation thereof will be carried out up to the desired number of copies within the number of the fed cut sheets without interruption.
In the conventional constructions (particularly, Japanese Laid-open Patent Application No. 112247/1982), the paper sheets are fed to the paper conveying section by rotation of paper feed roller means provided above the paper-containing section and then stopped at a predetermined position in the paper conveying section as the feed roller means in deenergized. Thus, the paper sheets should always be acted on by the feed roller means. Since the feed roller means is located externally of the paper conveying section, paper sheets of a length smaller than that of the paper conveying section cannot be used in such an arrangement.
In the construction of Japanese Laid-open Patent Application No. 112247/1982, the paper sheet feed to the paper conveying section is unstable since it is effected only by the use of feed roller means, resulting in easy paper jam.